1. Field of the Invention
The present invention relates to an image forming apparatus employing an electrophotographic system such as a laser printer or an electrophotographic system copying machine, and particularly to an image forming apparatus having no strip-off pawl installed as an auxiliary member which strips off recording media such as a recording sheet or an OHP sheet from the surface of a toner image support body such as a photosensitive body or an intermediate transfer body.
2. Related Art Statement
In an image forming apparatus 1 employing an electrophotographic system such as a laser printer or an electrophotographic system copying machine, as shown in FIG. 1, first, the surface of a photosensitive body 2 is charged to a fixed surface potential by a charger 3, and then, the surface of the photosensitive body 2 is exposed by an exposing device 4 such as a semiconductor laser to attenuate the surface potential, thus forming an electrostatic latent image. Then, a bias voltage is applied to the surface of a developing roller 6 of a developing device 5, a toner charged within the developing device 5 is adhered to an electrostatic latent image forming portion surface of the photosensitive body 2 and developed to form an image, thus displaying a toner image on the surface of the photosensitive body 2.
On the other hand, a recording paper P is taken out of a sheet cassette 7 by a feed roller 8, and carried to a transfer region by a carrying roller 9. In the transfer region, the recording paper P is charged by a transfer charger 10, and the toner image formed on the surface of the photosensitive drum 2 is transferred to the surface of the recording paper P. Next, the recording paper P is stripped off from the surface of the photosensitive body 2 by a strip-off charger 11 and carried to a fixing device 12. And, the toner image is fixed to the surface of the recording paper P by a fixing roller 13, after which it is discharged outside the apparatus by a discharge roller 14.
The toner remained on the surface of the photosensitive body 2 after transfer is cleaned from the surface of the photosensitive body 2 by a cleaning blade 16, is accumulated within a cleaner 15, and afterward, is recovered into a toner waste box.
Incidentally, as a member which strips off the recording paper P after transfer from the surface of the photosensitive body 2, generally, it is often to disposed, in addition to the strip-off charger 11, a strip-off pawl for assisting the former. This strip-off pawl is disposed for the purpose of preventing the recording paper P from being moved into the cleaner 15 erroneously. However, since the pawl is placed in contact with the surface of the photosensitive body 2, it rubs the surface of the photosensitive body 2 at the contact point to wear and damage it results in deterioration, thus possibly lowering the quality of an image.
Therefore, it is sometimes that for the purpose of preventing the recording paper P from being moved into the cleaner 15 without disposing the strip-off pawl, a paper moving-in preventing sheet having an extreme end thereof positioned in the vicinity of the surface of the photosensitive body 2 is disposed. However, when the recording paper P comes in contact with the paper moving-in preventing sheet, a toner not yet fixed is adhered to the paper moving-in preventing sheet, and the toner is adhered to the recording paper P being carried later to produce toner-foul on the surface of the recording paper P.
In view of the foregoing, it is often that in place of the paper moving-in preventing sheet, a star-wheel 21 of thin wall-thickness having a sharp projecting portion 21a is disposed as shown in FIG. 2. In the star-wheel 21, since only the projecting portion 21a comes in contact with the recording paper P, the toner not yet fixed is not adhered, and no toner-foul occurs on the surface of the recording paper P. Further, when the extreme end of the recording paper P comes in contact, it rotates easily, whereby the transfer of the recording paper P is stabilized, the paper jam and occurrence of creases of the paper surface can be prevented effectively.
The star-wheel 21 is disposed relatively parting from the surface of the photosensitive body 2 as shown in FIG. 2. Where the extreme end of the recording paper P passes through a normal carrying route, as shown by A in FIG. 2, when the extreme end or surface of the recording paper P comes in contact with a sharp projecting portion 21a of the star-wheel 21, the star-wheel 21 is easily interlocked and rotated in the direction of Axe2x80x2 to carry the recording paper P smoothly.
However, where the situation that the extreme end of the recording paper P passes through the unexpected route, as shown by B in FIG. 2, should occur, the recording paper P is curved or bent and the paper jam would occur. Further, since a recovery plate 17 attached to the cleaner 15 is in contact with the surface of the photosensitive body 2 at an angle for receiving a residual toner into the cleaner 15, the recording paper P tends to move into the cleaner 15 along the surface of the recovery plate 17, and the jam treatment where the recording paper P has been moved in is extremely difficult.
While in the foregoing, a description has been made of the case where the recording paper P is stripped off from the surface of the photosensitive body 2, it is noted that the same is true for the case where the recording paper P is stripped off from the surface of an intermediate transfer body, and is true for the case where recording media other than the recording paper P are stripped off.
An aspect of the present invention has been accomplished in an attempt of overcoming a conventional problem with respect to an image forming apparatus not provided with a strip-off pawl as an auxiliary member which strips off a recording medium from the surface of a toner image support body, and it is an object of an aspect of the invention to provide an image forming apparatus capable of effectively preventing a recording medium from being moved into a cleaner without occurrence of toner foul on the surface of a recording medium.
For achieving the aforementioned object, the image forming apparatus according to one aspect of the present invention comprises: a star-wheel having a sharp projecting portion, and disposing an auxiliary member which strips off the recording medium with a spacing between the surface of the toner image support body and an extreme end of the projecting portion held by a fixed distance, and an inversion preventing member formed from a synthetic resin sheet having flexibility and in which an extreme end thereof is placed in contact with the projecting portion of the star-wheel so that the start-wheel is not allowed to be rotated in the direction reversed to the direction of rotation where the recording medium passes through a normal carrying route.